Cement-based compositions enjoy broad application in construction materials, tile setting, wall and pool plasters, stucco, self leveling compounds, roofing tiles and cement patches. Concrete and like materials are produced from the alkaline earth metals typically by mixing portland cement with sand, gravel, and water. The reaction of the cement with the water produces among other things metal carbonates such as calcium carbonate. The calcium carbonate in the mixture is insoluble in water but reacts readily with most acids.
There has been a desire for some time to produce colored concrete to improve the decorative appearance of concrete. For example, U.S. Pat. No. 3,930,740 discloses tools for imprinting non-repeating stone patterns in fresh concrete to which color is added. U.S. Pat. No. 5,735,094 discloses a process for applying an ornamental coating comprised of liquid mortar which includes a color pigment. The addition of dyes and pigments to the cementitious materials has also enjoyed wide application in all of the above mentioned materials.
There are several processes for coloring or ornamenting a concrete surface that are known in the art. These include sweeping partially set concrete to produce a broom surface or adding a coloring agent that is mixed into the concrete blend. However, afterwards, a thorough clean-up of the applicator equipment is necessary, resulting in considerable labor and expense. This method is costly and inefficient, as coloring agents are expensive, become mixed throughout the concrete, and are only needed at the surface where they are visible. More elaborate surface treatments are known, including embedding stones varying in size or color into concrete areas by means of cement or resin.
One of the more common processes known in the art for coloring or staining concrete involves washing a concrete surface with an acidic solution containing a metallic salt. After application of the acidic staining solution and development of the color, a neutralizing agent is commonly applied to the stained concrete and a clear protection polymeric sealer costing is applied.
A second common method in the art of coloring concrete involves washing the concrete surface with an acidic solution to roughen or etch the surface; neutralize and rinse away the etching solution with a mixture of common baking soda and water; coloring the surface with a polymer based stain or paint, and finishing the surface with a clear coating.
Another known process involves washing a concrete surface with acidic solution to clean the concrete, applying a layer of polymers to the concrete surface, applying a first layer of an aqueous solution of cement and polymers to the coated concrete surface, applying a template with adhesive backing to selected regions of the first layer of cement and polymers, applying a second cement and polymer layer over the template and the first coating layer, applying colored materials to the second cement and polymer layer prior to the curing of the second layer, and removing the template to expose the colored concrete surface. A sealer may also be applied over the colored concrete surface.
However, these coating processes involve the use of highly corrosive acidic solutions, which are dangerous to handle. If the use of the acid is eliminated, the coloring of the concrete is not permanent and is prone to peeling and erosion. Consequently, there exists an unfulfilled need for a concrete coloring process that uses a permanent less corrosive coloring agent that results in a decorative, durable, coated concrete surface.